1. Field of the Invention
The invention relates to an all-purpose septic tank.
An all-purpose septic tank receives all of the domestic waste water, i.e. the sanitary waste water (from WC's) and the household waste water (from kitchens and bathrooms).
A septic tank must perform three functions: collect the water, liquefy, at least partially, the pollutants in the waste water and retain the solids and floating debris. In accordance with the most recent regulations applicable since 1982, a septic tank must be arranged so to avoid direct flow between the inlet and outlet devices and also prevent sediment and floating matter, for which a sufficient volume is retained, from being stirred up and carried along. The working height of the water must not be less than 1 m. It must be sufficient to allow a liquid zone inside which the effluent outlet device is located. The effluent inlet device must be dimensioned such that it does not form an obstruction of any kind and designed so as to avoid stirring up the separated matter. The depth at which the effluent outlet device is immersed must be such that it prevents entrainment of floating matter and limits entrainment of separated matter which may have been stirred up. The partition which may be placed inside the tank must be provided with orifices of adequate dimensions and arranged so as to prevent direct flow between the inlet and outlet devices.
2. Description of Related Art
Previously, the regulations restricted the use of septic tanks to sanitary waste water alone.
This change in the regulations has influenced developments in the state of the art.
Thus, from a first development in the prior art, where the use of septic tanks was limited to sanitary waste water, a septic tank is already known (French Patent No. 2,050,858), comprising a chamber divided into two compartments: an inlet compartment into which an effluent inlet pipe leads and an outlet compartment from which a clarified-water outlet pipe leads. Such a septic tank must also be provided with a purifying device consisting of a bacteria bed, an absorbant layer or an underground treatment system. This purifying device is often ineffective or is not used or does not even exist. Such a purifying device is illustrated, for example, in French Patent No. 2,057,419.
Various embodiments have been proposed for such septic tanks, with the following stated aims: to increase the strength of the septic tank (French Patent No. 2,054,970) by providing three continuous chambers inside it; to enable the construction of large-capacity septic tanks by means of partitioning (French Patent No. 2,110,681); to incorporate a filter inside the actual septic tank (French Patent No. 2,158,165); to enable easier and more rapid manufacture of the septic tank (French Patent Nos. 2,215,517, 2,482,157 and 2,496,143); finally, to enable the septic tank to be disassembled and easily transported (French Patent No. 2,386,651).
It is also envisaged (French Patent Nos. 2,110,746, 2,307,922 and 2,427,438) to arrange two independent subassemblies for treating sanitary waste water and household waste water, next to each other in a single assembly, so as to comply with the regulations formerly in force.
The most conventional structure for these septic tanks consists in the inlet compartment having a volume which is larger (in particular twice as large) as the outlet compartment, the two compartments being separated from each other by a transverse partition which is located inside the chamber and projects beyond the liquid level so as to prevent floating particles passing from the first to the second compartment. An opening is provided in the partition, in particular in its middle region, so as to allow the water to pass from the first to the second compartment, while ensuring that the first compartment performs its clarifying function. The inlet and outlet consists most commonly of pipes which are bent downwards and located at the same height. A manhole is usually provided in the chamber cover.
The most recent regulations on all-purpose septic tanks designed to receive all domestic sewage led to a second development.
Manufacturers first of all purely and simply proposed to increase the volume of the tanks so as to cater for the increased amount of waste water to be treated. However, this solution proved to be ineffective because the hydraulic operation of an all-purpose septic tank is completely different from that of a conventional septic tank intended for sanitary waste water alone. This resulted in the removal of sludge, particles, greasy substances, etc. by the septic tank, causing clogging of the land treatment system located downstream of the septic tank.
In order to overcome this drawback, it was proposed to combine with the septic tank, immediately downstream of it, an operation indicator which signals entrainment of the sludge, i.e. incorrect operation of the septic tank. This operation indicator is called, depending on the situation, a prefilter, colloid separator or coarse-particle filter. This combined arrangement consisting of an all-purpose septic tank and colloidal prefilter is described in French Patent Nos. 2,503,216 and 2,499,125. The latter French Patent No. 2,499,125 envisages, moreover, the possibility of cleaning the filters by reversing the direction of flow of water. However, the existence of a separate prefilter or colloid separator has given rise to certain problems and this is why it was then proposed to incorporate the said filter inside the all-purpose septic tank. This gave rise to allpurpose septic tanks in which the prefilter or colloid separator is situated inside the second compartment (French Patent Nos. 2,523,618, 2,531,635, 2,550,566 and 2,554,843). In these septic tanks, the outlet leads directly to the operation indicator usually fixed, on the one hand, to the chamber cover and, on the other hand, to the separating partition. Two manholes are provided so that access can be gained to the first compartment and the operation indicator, respectively. Numerous detailed embodiments of such all-purpose septic tanks with an incorporated prefilter or colloid separator have been proposed. Experience shows that, using the operation indicator, it is possible to detect clogging of the tank and hence the need for drainage before the land treatment system has itself become clogged up. On the other hand, these all-purpose septic tanks do not perform in an optimum manner their functions of liquefying and retaining solid matter, thereby giving rise to increased maintenance costs.